In my co-pending patent application, Ser. No. 560,350, filed Mar. 21, 1975 now U.S. Pat. No. 3,968,839, of which this patent application is a continuation in part, it is pointed out that there are many hydrocarbon producing wells incapable of sustaining a flow velocity within the production tubing which is in excess of the critical flow rate of the well. Hence the velocity is insufficient to prevent generation of a liquid column or hydrostatic head which accumulates within the production tubing and eventually causes the well to load up. These wells usually are referred to as low volume gas wells or high GOR (gas-oil ratio) oil wells. In such an instance, liquid progressively accumulates within the production string, and eventually the accumulated hydrostatic head will attain a value which essentially "shuts in" or "kills" the well.
Kicking off a dead well is expensive and wasteful, because a technician must blow down the well to atmospheric pressure in order to provide sufficient pressure differential for overcoming the effective hydrostatic head. Sometimes the additional step of "swabbing" is required in order to re-establish the flow.
The present known methods of pulse flowing a low GOR type well is carried out by employing a surface control valve and equipment which utilizes a time cycle or a surface pressure controller. The well is shut in for a finite time interval to enable the downhole formation and borehole to be recharged, whereupon the gas associated with the reservoir is allowed to be compressed to a value which overcomes the hydrostatic head of the wellbore. When the compressed gas is released, the resultant gas expansion establishes a flow rate of a sufficient velocity to unload the accumulated liquids. The well is allowed to flow down to a predetermined rate, whereupon the well is shut in again, and the cycle of operation is repeated.
Pulse flowed, low volume wells must rely upon pressure being effected each flow cycle within the entire tubing string and annulus, which often causes the outflow lines to be momentarily overloaded. Accordingly, this undesirable solution also causes other problems, such as difficulty in correctly attaining proper gas measurements at the meter run, and interference with the operation of other downstream equipment and apparatus.
In the above-noted patent (U.S. Pat. No. 3,968,839), a spring setting on the pilot was employed to set a fixed opening pilot pressure. This expedient fails to take into account the possibility of fluctuating surface line pressure or changes in downhole tubing pressure; and therefore, should the pressure in the line located downstream of the well head change, this change in pressure is reflected on the bottom hole pressure. Therefore, should this downstream pressure change drastically, the set pressure of the pilot could cause the downhole valve device to open at an inappropriate bottom hole pressure differential.
Accordingly, it is desirable to provide the tool of my previous invention with means by which changes in the downstream pressure are taken into account respective to opening of the pilot valve.
Accordingly, it is desirable to have made available a system and method of subsurface well control and operation which is responsive to changes in both surface and subsurface pressures, and which employs a minimum bottom hole pressure differential requirement for producing the well so that an optimum amount of gas and liquid can be attained from the wellbore.